|Publication number||US7474728 B2|
|Application number||US 10/518,848|
|Publication date||Jan 6, 2009|
|Filing date||Jun 19, 2003|
|Priority date||Jun 28, 2002|
|Also published as||DE10228941A1, EP1519682A1, US20060171502, WO2004002316A1, WO2004002316A8|
|Publication number||10518848, 518848, PCT/2003/2904, PCT/IB/2003/002904, PCT/IB/2003/02904, PCT/IB/3/002904, PCT/IB/3/02904, PCT/IB2003/002904, PCT/IB2003/02904, PCT/IB2003002904, PCT/IB200302904, PCT/IB3/002904, PCT/IB3/02904, PCT/IB3002904, PCT/IB302904, US 7474728 B2, US 7474728B2, US-B2-7474728, US7474728 B2, US7474728B2|
|Inventors||Jens-Peter Schlomka, Geoffrey Harding|
|Original Assignee||Koninklijke Philips Electronics N.V.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (8), Non-Patent Citations (1), Referenced by (8), Classifications (19), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The invention relates to a computed tomography apparatus (CT apparatus) for imaging by means of radiation having traversed an object to be examined (that is, directly transmitted radiation), as well as by means of radiation scattered by the object to be examined.
A CT apparatus of this kind is known, for example, from EP 1 127 546. It comprises essentially a radiation source for generating a fan beam which traverses an object to be examined, as well as a two-dimensional detector arrangement which consists of a plurality of individual detector elements which are arranged in rows and columns in conformity with the length and the width, respectively, of the cross-section of the fan beam. The number of columns generally is substantially larger than the number of rows and the longitudinal dimension of the detector arrangement is substantially larger than its dimension in the direction of the width of the cross-section of the fan beam.
The angle of aperture of the fan beam in the direction of its width (that is, in the direction perpendicular to the fan plane) can be varied by means of diaphragm devices. When the radiation having traversed the object to be examined (the transmitted radiation) is to be detected as well as the radiation scattered by the object, such a diaphragm device is selected that a comparatively small width of the fan beam is obtained. In that case the directly transmitted radiation is detected essentially by the central row of the detector arrangement, whereas the scattered radiation, being directed away from the plane of the fan beam to both sides, is incident on the outer rows of the detector arrangement.
In order to optimize the pulse momentum transfer spectrum, furthermore, a collimator arrangement which consists of a plurality of lamellas is arranged between the object to be examined and the detector arrangement, which lamellas subdivide the fan beam into a number of segments so that the detector elements that are situated in one column are struck by transmitted and scattered radiation from the same segment of the object to be examined.
However, it has been found that the detection of the scattered radiation by means of in particular those detector rows which adjoin the central row (rows) is disturbed by crosstalk due to the incidence of the transmitted radiation which is significantly more intense for given objects to be examined. This problem may become more serious notably when use is made of detector arrangements having a comparatively small width such as included in some known CT apparatus.
If, moreover, single-row detector arrangements are used, generally speaking, detection of the scattered radiation is even impossible by means of such CT apparatus.
Therefore, it is an object of the invention to provide a CT apparatus of the kind set forth whereby the radiation scattered by an object to be examined can be detected at least substantially without being affected by radiation having traversed the object to be examined (that is, transmitted radiation).
It is also an object of the invention to provide a CT apparatus whereby the radiation scattered by an object to be examined can be detected at least substantially without being affected by radiation having traversed the object, that is, even when use is made of a detector arrangement comprising only one detector row or only a few detector rows.
Finally, it is also an object of the invention to provide a CT apparatus whereby transmitted and scattered radiation (CT and CSCT mode) can be detected simultaneously when use is made of a multi-row detector arrangement, without the measurement of the scattered radiation being significantly affected by crosstalk from the transmitted radiation.
In conformity with claim 1 the object is achieved by means of a computed tomography apparatus which includes a radiation source, a detector arrangement and a device with which (transmitted) radiation having traversed an object to be examined can be stopped at least to such an extent that its intensity which is incident on the detector arrangement does not significantly exceed the intensity of radiation scattered by the object to be examined and incident on the detector arrangement.
It has been found that the required degree of stopping is dependent essentially on the quality of the detector arrangement and notably on the crosstalk attenuation thereof as well as on the desired image quality. The less the crosstalk between neighboring detector elements or detector rows and the lower the requirements imposed on the image quality, the lower the adjusted degree of said stopping may be.
A special advantage of this solution resides in the fact that the simultaneous detection of transmitted and scattered radiation can also be carried out by means of detector arrangements which do not satisfy severe requirements in respect of their crosstalk properties, so that additionally costs can be saved.
It is to be noted that U.S. Pat. No. 6,175,117 discloses a tissue analysis device which includes a beam-forming device for the analysis of substances in the breast as well as a detector for the detection of radiation transmitted and scattered by the breast, a filter which comprises a number of areas which are transparent to radiation and absorb the radiation being arranged in front of the filter. Apart from the fact that this device is not a computed tomography apparatus, this filter structure is provided for a detector arrangement which has a comparatively large surface area which cannot solve the problem to be solved in accordance with the invention, so that the cited publication is not considered to be of relevance.
The dependent claims relate to advantageous further embodiments of the invention.
The embodiments in conformity with the claims 2 and 7 offer the advantage that the transmitted and the scattered radiation can also be detected simultaneously when the detector arrangement is suitably proportioned.
The embodiment in conformity with claim 3 represents a particularly economical solution.
The embodiments disclosed in the claims 4 and 6 can also be implemented at a later stage, while using limited means only, in already existing computed tomography apparatus.
The embodiments disclosed in the claims 5 and 9 enable measurement of the scattered radiation at different angles relative to an object to be examined.
Further details, features and advantages of the invention will become apparent from the following description of preferred embodiments which is given with reference to the drawing. Therein:
The detector arrangement 16 is composed of a plurality of detector elements which are arranged in the form of a matrix which comprises at least one row and a plurality of columns. The detector rows extend in the circumferential direction of the gantry 1 whereas the columns extend perpendicularly thereto. The detector arrangement 16 and the second collimator 32 are also attached to the gantry 1.
The object 13 to be examined can be displaced in the direction of the axis of rotation 14 of the gantry by means of a second motor 5.
Using a first drive unit 31 a, the first collimator 31 or the radiation source S can be displaced in a direction perpendicular to the plane of the gantry 1. Alternatively or additionally, there is provided a second drive unit 32 a whereby the second collimator 32 and the detector arrangement 16 can also be displaced in a direction perpendicular to the plane of the gantry 1.
A control unit 7 is provided for controlling the motors 2, 5 and the drive units 31 a, 32 a, said control unit itself being connected to an image processing computer 10. The detector arrangement 16 is also connected to the computer 10 which processes the detector signals and forms an image of the object 13 to be examined on a monitor 11.
As is also shown in
Alternatively, the radiation source S and the collimator 31 may also be proportioned in such a manner that a conical radiation beam is generated.
In order to optimize the pulse momentum transfer spectrum it is again possible to arrange, as described in the cited EP 1 127 546, a collimator arrangement in the form of a plurality of lamellas between the object 13 to be examined and the detector arrangement 16, which lamellas subdivide the radiation beam 41 into a number of segments in such a manner that the detector elements present in one column are struck by transmitted and scattered radiation from the same segment of the object 13 to be examined. Therefore, the publication EP 1 127 546 is incorporated in this description by way of reference.
As can also be seen in
In the second embodiment as shown in
In the embodiment shown in
The above three embodiments enable unobstructed detection and evaluation of the scattered radiation 41 b by means of a single-row detector arrangement as well as by means of a multi-row detector arrangement 16.
The principles illustrated in the
However, if the transmitted radiation and the scattered radiation are to be detected simultaneously, preferably the first embodiment as shown in
As opposed to the first embodiment as shown in
To this end, the central region 321 of the second collimator 32 contains a material of an appropriate thickness which absorbs the radiation in the fourth embodiment as shown in
In the fifth embodiment as shown in
For the proportioning of the absorptivity of the central region 321 or the width and length of the opening in this region 321 the fact must be taken into account that, in dependence on the object density, the intensity of the transmitted radiation 41 a may be a factor of from 10 to 1000 higher than the intensity of the scattered radiation 41 b. The attenuation of the transmitted radiation intensity should preferably also be of this order of magnitude, so that the transmitted radiation 41 a and the scattered radiation 41 b are incident on the detector arrangement 16 with approximately the same intensity.
If necessary, of course, this principle can also be reversed when the central region 321 is arranged in the path of the scattered radiation in order to attenuate the scattered radiation 41 b relative to the transmitted radiation 41 a for some reason.
A special advantage of the invention resides in the fact that it enables switching over between the imaging and evaluation on the basis of the transmitted radiation (CT mode) and the imaging and evaluation on the basis of the coherent scattered radiation (CSCT mode) during the examination of an object. Significantly better examination results can thus be achieved. This holds for diagnoses in the medical field as well as for the examination of materials.
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|U.S. Classification||378/6, 378/7, 378/86|
|International Classification||A61B6/03, A61B6/06, A61B6/02, G01N23/201, G01N23/00|
|Cooperative Classification||A61B6/4417, A61B6/4291, A61B6/032, A61B6/027, A61B6/483, A61B6/06|
|European Classification||A61B6/03B, A61B6/44F, A61B6/48F, A61B6/42J, A61B6/06|
|Aug 20, 2012||REMI||Maintenance fee reminder mailed|
|Jan 6, 2013||LAPS||Lapse for failure to pay maintenance fees|
|Feb 26, 2013||FP||Expired due to failure to pay maintenance fee|
Effective date: 20130106